On Feb. 9, 1988, U.S. Pat. No. 4,724,400, entitled "Linear Amplifier Assembly" was issued in the name of G. G. Luettgenau to TRW Inc. (the "400 Patent"). Such patent is treated herein solely as a publication. The disclosure of the '400 patent as a publication is, however, incorporated herein by reference and made a part hereof.
The '400 patent shows and describes a microwave splitter-combiner apparatus comprising a cylindrical stack of vertically superposed circular metallic plates defining within the stack an upper splitter waveguide and a lower combiner waveguide. Each such waveguide comprises a pair of vertically spaced metallic walls and a chamber between and bounded by such walls and providing a passage through which microwaves propagate, the chamber being essentially in the form of a horizontal cylindrical disc. In the splitter waveguide, the microwaves travel through its cylindrical chamber from its center radially outward while, in the combiner waveguide, such travel in its chamber is radially inward towards the center of the chamber.
Disposed on a plate member providing a top closure for the mentioned stack is a set of twenty r.f. amplifier operating units each essentially in the shape of a rectangular block. The twenty units are equiangularly spaced in carousel fashion around the top of such member in respective radial planes which are vertical and pass through the vertical axis of the stack.
Each of such twenty r.f. amplifier units is coupled to the splitter waveguide by an input coaxial connector and to the combiner waveguide by an output coaxial connector. In the operation of the apparatus, high frequency electromagnetic energy is fed to the splitter waveguide's center, travels therefrom radially outward through the waveguide's chamber to the twenty input connectors and is then fed upward by them to the twenty amplifiers which operate in parallel to amplify such energy. The amplifier energy is then fed via the twenty output connectors to points in the combiner waveguide's chamber which are radially outward of the chamber's center. From those points the energy travels as waves radially inward through the chamber to its center to there be combined and provide an amplified output from the apparatus.
In the apparatus of the '400 patent, the input microwave energy is supplied to the upper splitter cavity via an input coupling unit described in that patent as a coaxial type connector and the amplified microwave energy is tapped off from the lower combiner cavity by another similarly described coupling unit. Both such connectors are best depicted in FIG. 5a of the patent, and the inner conductor of each of such type connectors is shown in that figure as being a constant diameter smooth-surfaced pin and as having its front end received in a constant diameter smooth-bore hole formed in one of the metallic cavity bounding plates.
Improvements on the splitter-combiner apparatus of the '400 patent are disclosed in my co-pending U.S. patent application Ser. No. 472,160, filed Jan. 30, 1990 and assigned to the assignee hereof, and incorporated herein by reference and made a part hereof (hereafter referred to as "Myer 18"). Among such improvements is a construction of the apparatus wherein the top and bottom sides of, respectively, the upper splitter cavity and the lower combiner cavity are bound by upper and lower rigid aluminum plates, whereas the bottom and top sides of, top sides of, respectively, the upper cavity and the lower cavity are bounded by, respectively, upper and lower aluminum sheet metal dishes separated from each other by a gap. For each of such cavities, there is a coaxial coupler unit having an outer conductor coupled to the rigid plate on one side of that cavity, and having, also, an inner conductor passing through a port in such plate at the radial center of the cavity, and then extending along the axis of the cavity vertically through it to contact the sheet metal dish on the cavity's opposite side.
Such coupler unit may serve as an input or output for microwaves, as the case may be, and the coupler unit may be as disclosed in U.S. Pat. No. 5,001,443 for "Coaxial-Waveguide Assemblages", issued Mar. 19, 1991 in the name of James N. Martin and assigned to the assignee hereof and incorporated herein by reference and made a part hereof.
Because the mentioned dish is of sheet metal, it is somewhat deformable so that the dish has a portion capable of variable axial spacing with a corresponding portion of the rigid plate on the cavity's opposite side. Advantage is taken of that fact to provide for tuning of the resonant frequency of the cavity in a manner as follows.
The rigid plate has therein a vertical threaded hole radially offset from the cavity axis. A threaded dielectric screw extends vertically from the outside of such plate through such hole and beyond it to a front end in contact with the dish. Turning of the screw in one direction advances the screw in the hole to displace the dish away from the plate bounding the other side of the cavity. Subsequent displacement, if any, of the dish towards such plate is effected by having a compression spring in a compressed state in the gap between the two metal dishes, and by using the spring force to produce such displacement while concurrently turning the screw in the angular direction permitting that displacement to take place. The variation caused by so displacing the dish in either vertical direction will vary the spacing between portions of the plate and dish on opposite sides of the cavity so as to vary its resonant frequency.
While such mode of tuning the cavity is satisfactory, it has the shortcomings that the insulative screw is not as dimensionally stable as is preferable, the screw is off-axis to tend to produce asymmetry in the deformation of the dish as its center portion is displaced, an asymmetry in the electrical characteristics of the cavity may be produced by the presence therein of the screw.